Vacuum forming of heated glass sheets against a curved mold surface has been performed for many years. Such vacuum forming is usually performed by drawing a vacuum within openings in the mold surface. The extent of vacuum utilized is normally on the order of about several to 10 inches (about 10 to 25 cm.) water column. Such a conventional vacuum can be provided by commercially available hot operating fans that are positioned within a heated environment in which the vacuum forming is performed and can also be provided by a gas jet pump such as disclosed by U.S. Pat. No. 4,222,763 McMaster wherein a primary gas flow is introduced into a passageway through jet openings which have axial and circumferential components that are substantially tangent to the inner surface of the passageway such that the primary gas flow induces a secondary gas flow that generates the vacuum through suitable communication passageways.
Prior art glass sheet vacuum forming systems are disclosed by U.S. Pat. No. 3,778,244 Nedelec et al; U.S. Pat. No. 4,661,141 Nitschke et al; U.S. Pat. No. 4,711,653 Frank et al; U.S. Pat. No. 4,746,348 Frank et al; and U.S. Pat. No. 4,859,225 Kuster et al.